1. Field of the Invention
This invention relates to a fluid flow control system for use with a heat exchange apparatus comprising a system charge control device to regulate the active charge of refrigerant in the system and the flow of refrigerant between the condenser and evaporator.
2. Description of the Prior Art
Numerous heating and cooling apparatus including condensors, compressors and evaporators have been developed for use with fluorocarbon refrigerants such as Freon. For example, U.S. Pat. No. 3,965,694 discloses an apparatus for heating or cooling including a first heat exchange to transfer heat between the refrigerant and the atmosphere and a second subterranean heat exchange to transfer heat between the earth and the refrigerant. A capillary tube restricting device is positioned in the refrigerant line between the first and second heat exchanges to liquefy the refrigerant before reaching the subterranean heat exchange. U.S. Pat. No. 2,513,373 discloses a heat pump for heating or cooling a fluid utilizing a closed circuit refrigerant loop. A closed circuit water line circulates water through a pair of subterranean heat exchanges. A heat exchange which is coupled to both the closed circuit refrigerant loop and the closed circuit water line transfers heat energy between the independent water and refrigerant systems.
U.S. Pat. No. 2,529,154 discloses a solar heating system where water is circulated within a closed system coupled to a solar energy heat absorber while the refrigerant is circulated through a second closed system.
Other examples of the prior art are disclosed in U.S. Pat. Nos. 1,958,087; 2,448,315; 2,512,869; 2,693,939; 2,968,934; 3,175,370; 3,226,940; 3,315,481; 3,392,541; 3,499,296; 3,564,862; 4,012,920; 4,049,407; 4,091,994; 4,187,695; 4,194,367; 4,320,630; 4,488,413; France No. 487762 and Sweden No. 59350.
In any refrigeration and heat pump system the three major components; compressor, condenser and evaporator, require certain refrigerant conditions in order to operate at optimum efficiency. For optimum efficiency the compressor requires a dry or totally evaporated refrigerant with little or no superheat at the compressor inlet. The condensor requires the refrigerant outlet pressure to be just sufficient to force all fluid to condense or become liquid just as the refrigerant reaches the outlet or a point near the outlet if subcooling is desired. The evaporator should, on the other hand, receive only liquid refrigerant at the evaporator inlet. Evaporation should be complete just as the refrigerant reaches the outlet. In this condition, the evaporator is said to be "flooded". However, no unevaporated refrigerant should leave at the outlet.
In conventional refrigeration systems, refrigerant flow controls have many shortcomings which cause inefficient operation of the three major components previously described. For example, thermal expansion valves control the output of the evaporator and input to the compressor inefficiently as the superheat at the compressor inlet, evaporator outlet is held at at 12.degree. F. Such valves are unable to control conditions in the condensor at all. Electric expansion valves exhibit similar shortcomings except that they are able to hold the superheat at the compressor inlet closer to the desired 0 degrees F. Both thermal and electric expansion valves are unable to control systems with relatively long evaporators such as long supermarket coolers and earth tap evaporators, as these systems "hunt" wildly.
Capillary tubes, "automatic" expansion valves and fixed orifices control the conditions in all three major components very inefficiently. This is especially true in systems having condensors and/or evaporators with wide temperature and pressure excursions during each run cycle.
With conventional flow controls "blow-through" of uncondensed vapor at the condensor outlet is not uncommon. Conventional flow controls are unable to provide fixed subcooling including zero subcooling in the condenser or to provide a continuously flooded evaporator without returning unevaporated refrigerant to the compressor.
It is therefore an object of the present invention to provide subcooling and blow-through control, and to maintain liquid refrigerant flow from the condenser at exactly the rate at which the condenser and the entire system is able to produce liquid condensate.
It is further an object of the present invention to provide a constant smooth flow of liquid refrigerant to the evaporator and a constant smooth flow of vapor refrigerant, of low superheat, from the evaporator to the compressor providing an efficient, effective and reliable fluid flow control system. In short, it is an object of the present invention to provide the desired optimum refrigerant conditions at the condenser, evaporator and compressor at all times during operation.